(a) Field of the Invention
The present invention relates to a method and apparatus for retransmission.
(b) Description of the Related Art
Among retransmission schemes, a Hybrid Automatic Repeat Request (HARQ) scheme is a combined transmission scheme of a Forward Error Correction (FEC) and an Automatic Repeat Request (ARQ) scheme. The HARQ scheme can be classified into a synchronous HARQ scheme and an asynchronous HARQ scheme according to the transmission timing of a retransmission packet. The synchronous HARQ scheme is a scheme in which a retransmission packet for an initial transmission packet is transmitted at a predetermined timing, which is applicable to uplink HARQ retransmission. The asynchronous HARQ scheme is a scheme in which a scheduler of a base station determines a transmission timing of a retransmission packet, which is applicable to downlink HARQ retransmission. The HARQ scheme may be classified into an adaptive HARQ scheme and a non-adaptive HARQ scheme according to changes in the amount and position of resources to be allocated. The adaptive HARQ is a scheme in which the amount and position of resources to be allocated can be changed. The non-adaptive HARQ is a scheme in which the amount and position of resources to be allocated are fixed. A wireless communication system can achieve a high scheduling gain and the effect of high speed data transmission by properly combining the synchronous and asynchronous HARQ schemes and the adaptive and non-adaptive HARQ schemes and using low signaling overhead.
Regarding a downlink (DL) HARQ operation in which a base station (BS) transmits a data burst in a downlink (DL), first of all, the base station transmits, to a terminal, control information including resource allocation information and an HARQ subpacket which is an encoded data burst. The control information may be included as an information element (IE) in a MAP. The MAP may be, for example, a Down Link Basic Assignment Advanced-MAP (DL B-A-A-MAP). The terminal having received the data burst decodes the data burst using the control information, and determines a transmission timing of a feedback signal and sends an ACK (positive acknowledgement) message or an NACK (negative acknowledgement) message to the base station.
Regarding an uplink (UL) HARQ operation in which a terminal (mobile station MS) transmits a data burst in an uplink (UL), the terminal receives control information including resource allocation information from a base station, and encodes the data burst using the received control information. After that, the terminal transmits an HARQ subpacket which is the encoded data burst to the base station at a predetermined transmission timing. At this point, the control information may be included in a MAP. The MAP may be, for example, an Up Link Basic Assignment Advanced-MAP (UL B-A-A-MAP). Then, the base station decodes the received data burst, and sends an ACK message or NACK message, as a feedback signal, to the mobile station. If the terminal receives the NACK message, the mobile station retransmits the data burst at a predetermined transmission timing.
A transmission time unit used in an HARQ operation is a Transmission Time Interval (TTI). The TTI is the duration of the transmission of the physical layer for a packet encoded over a radio air interface. The TTI is expressed as an integer number of subframes. For example, 1TTI equals to an amount of time corresponding to one subframe. A data burst may be transmitted in at least one subframe. In general, the number of subframes occupied by the data burst can be denoted by TTI. The transmission of the data burst in one subframe is referred to as 1TTI transmission or default TTI transmission, and the transmission of the data burst on continuous subframes is referred to as long TTI transmission.
In this manner, the base station and the terminal determine a transmission timing according to a predetermined transmission timing determination method and perform their corresponding HARQ operation. Thus, even if there are enough resources, the corresponding HARQ operation has to be performed after waiting until a settled transmission timing is reached. Accordingly, the transmission timing of a feedback signal may be unnecessarily delayed depending on the method of determining a transmission timing.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.